GENERAL PATTERNS IN THE SUMMER DISTRIBUTION OF EARLY JUVENILE OMMASTREPHID SQUID OFF EASTERN AUSTRALIA (MOLLUSCA, CEPHALOPODA) Malcolm Dunning To cite this version: Malcolm Dunning. GENERAL PATTERNS IN THE SUMMER DISTRIBUTION OF EARLY JUVE- NILE OMMASTREPHID SQUID OFF EASTERN AUSTRALIA (MOLLUSCA, CEPHALOPODA). Vie et Milieu / Life & Environment, Observatoire Océanologique - Laboratoire Arago, 1985, pp.163- 168. hal-03022060 HAL Id: hal-03022060 https://hal.sorbonne-universite.fr/hal-03022060 Submitted on 24 Nov 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. VIE MILIEU, 1985, 35 (3/4) : 163-168 GENERAL PATTERNS IN THE SUMMER DISTRIBUTION OF EARLY JUVENILE OMMASTREPHID SQUID OFF EASTERN AUSTRALIA (MOLLUSCA, CEPHALOPODA) Malcolm DUNNING Maritime Estate Management Branch, Quensland National Parks & Wildlife Service, P.O. Box 190, Brisbane North Quay, Queensland 4000 Australia CEPHALOPODA ABSTRACT. — Larval squid were sampled in three surveys off the eastern Austra- OMMASTREPHIDAE lian coast in January, March and May 1983. Ommastrephid larvae were abundant and LARVAL SQUID occurred at over 90 % of stations. Although identification to species level has not so EASTERN AUSTRALIA far been possible for the majority of spécimens, gênerai patterns of distribution with DISTRIBUTION respect to latitude and bottom depth are presented. CEPHALOPODA RÉSUMÉ. — De jeunes Céphalopodes planctoniques ont été échantillonnés au large OMMASTREPHIDAE de la côte Est de l'Australie en janvier, mars et mai 1983. Les « larves » d'Ommas- LARVES tréphidés étaient abondantes et présentes dans plus de 90 % des stations. Bien que AUSTRALIE EST l'identification des spécimens au niveau de l'espèce n'ait pas été possible jusqu'ici, DISTRIBUTION du moins pour la majorité des individus récoltés, quelques aspects généraux de la distribution des animaux en relation avec la latitude et la profondeur peuvent être dégagés. species known from the east coast at that time, INTRODUCTION Nototodarus gouldi (McCoy, 1888). Because of the limited size of the collection, géographie and seaso- Eleven species of the commercially important nal distribution patterns could not be described. squid family Ommastrephidae are known to occur The study described here aimed to obtain preli- off the eastern Australian coast (Nesis, 1979; Oku- minary information on the relative abundance of tani, 1980; Lu & Dunning, 1982; Dunning & Brandt, larval ommastrephid squid across the continental 1985; Dunning, In Prep.). While the distribution and shelf and slope off central eastern Australia and to relative abundance of adults are now relatively well assess any changes in relative abundance with lati- known, few studies have been directed at larval and tude and at différent times during the summer. early juvénile stages of thèse species in Australia Because this area is dominated by a western boun- waters. dary current, water mass associations were also Pélagie cephalopods collected by opportunistic expected to be important and detailed hydrographie plankton tows between the southern Great Barrier information was sought. Reef and southeast Tasmania were described by Broad distributional patterns for species groups Allan (1945). Ommastrephid larvae and early juvéni- only are presented here; detailed species distributio- les were outnumbered in the small collection only by nal patterns require identification of small larvae to "Pyrgopsis pacifiais (Issel)" [probably Leachia spp.] lower taxonomic units than has so far been possible and ail were referred to the only ommastrephid with this collection. 164 M. DUNNING Unless otherwise indicated, standardized values are used throughout this paper. METHODS Sampling was undertaken on each occasion from south to north to counter the possibility of towing in the same water mass in the southward flowing Early juvénile cephalopods were collected during current. On transects at 34°, 32°, 30° and 28°S on the three eight-day surveys undertaken between 28° and January and March surveys, paired day and night 34°S off the eastern Australia coast in January, samples were taken at each of the eight stations March and May 1983 (Fig. 1). Eight sampling during the same 24 hour period. Information on stations were located along transects roughly per- température, salinity, phosphates, nitrates, silicates pendicular to the continental slope at each degree and oxygen along each transect was obtained using of latitude nominally at bottom depths of 50, 100, expendable bathythermographs and a Neil Brown 200, 400, 1 000 and 2 000 mètres and at stations 5 CTD with rosette sampler. and 10 nautical miles east of the 2 000 m station. Concurrent 30 minute surface tows using 500 (j.m Larval ommastrephid squid are characterized by 50 cm paired Bongo nets and double oblique tows the fusion of the tentacles into a proboscis, persis- using a 500 um 1 m bridleless larval tuna net (FAO, ting from hatching to "metamorphosis" at between 1966) were undertaken at each station. Nominal 5 and 10 mm ML. Further identification was un- towing speed was 1.5 m sec"' (3 knots) with oblique dertaken using the following characters : tows to 150 m where bottom depths exceeded 200 m 1) the diameter of the latéral suckers on the probos- and to 10 m above the bottom in shallower water. cis tip; 3 Catches were standardized to numbers per 1 000 m 2) the location and size of light organs on the using Rigosha flowmeter counts from each net. ventral surface of the eyes and intestine; 3) the length of the proboscis relative to mantle length until the commencement of splitting to form the tentacles; 4) the length of the tentacles just prior to splitting relative to longest arm length. Larvae with mantle lengths greater than 4 mm could generally be identified at least to genus using the above characters. However, the vast majority of the spécimens collected during the study were less than 3 mm ML and thèse spécimens have been separated into three major species groups as shown in the following table : Sucker Proboscis Species included dianieters length Group 1 > ML Ommastrephes bartrami Ornithoteuthis volatilis Nototodarus hawaiiensis Group 2 > ML Sthenoteuhis spp. Group 3 < ML Eucleotheuthis luminosa Nototodarus gouldi Todaropsis eblanae Todarodes pacificus Larvae of Todarodes Jîlippovae would fall into Group 3 morphologically but the known distribution of mature adults (Dunning & Brandt, 1985) makes it unlikely that this species is represented in the collections. No spécimens of Hyaloteuthis pelagica (which have light organs présent on the eyes and intestine from 1.5 mm [Harman & Young, 1985, this vol.]) were represented among the spécimens less than 3 mm ML. Fig. 1. — Study area showing the East Australian Current and the transects along each degree of latitude. AUSTRALIAN JUVENILE OMMASTREPHID SQUID : SUMMER DISTRIBUTION 165 RESULTS Seasonal and latitudinal distribution of larvae Numerically, ommastrephids were the dominant Océanographie patterns cephalopod larvae represented in the collections and occurred at over 90% of the stations sampled. Throughout the sampling period, the area was Larvae were more abundant in March than in either dominated by the East Australian Current (EAC) January or May with a mean overall catch rate from (Hamon, 1965; Boland & Church, 1981), carrying oblique tows of 15.7 individuals (standard déviation tropical Coral Sea water southward along the off- [SD] 28.5). This compared with 4.3 (SD 6.4) and 7.5 shore edge of the continental shelf to a point between (SD 8.9) respectively in January and May. A similar 31° and 32°S where it turned eastward to form the pattern was évident in surface samples. In January, Tasman Front (Stanton, 1981). During the January the average catch rate was 5.5 individuals (SD 8.4), and March surveys, the EAC was évident at the in March 24.3 (SD 60.9) and in May, 9.2 (SD 13.9). slope as far south as 32° but in May, had moved The highest catch of 450 individuals per 1 000 m3 away from the slope just to the north of 31°S. A was obtained from a surface sample taken at 32°S température profile throught the current at 32°S in in 100 m depth in March. March is shown in figure 2. Anticyclonic warm core Species group 1 overwhelmingly dominated sam- 'eddies' pinched off from the EAC often occur south ples from the first two surveys, comprising more of 32°S but were not encountered during the sam- than 99 % of ail individuals. Ommastrephes bartrami pling period in the area surveyed. and Ornithoteuthis volatilis were represented among the larger larvae and juvéniles collected. By contrast, 153°E 153-30 44% of spécimens caught during the May cruise 0 —_J— . l were from species groups 2 and 3 and larger spéci- 23=^ mens of Ornithoteuthis volatilis and Sthenoteuthis (probably oualaniensis) were positively identified. ~X N>0\ 19 — Représentatives of species group 3 outnumbered >s \ \ \ 17 those of group 2 by approximately 4 : 1 in this - survey. 32°S 13 Mean catches combining ail depth strata for each AA >i\ \N \ A \ n degree of latitude are shown in Table 1. In January, highest mean catches were at 33°S, in March at 32°S 500 Fig. 2. — Température profile through the EAC at 32 °S, Table I. — Mean catches standardized to 1 000 m3 by March 1983. latitude for the 1983 larval surveys. Latitude Oblique tows Surface tows Total Surface currents were strongest in ail three sur- January survey veys at the edge of the continental shelf (400-1 000 m 28°S 4.7 3.2 4.0 29°S 5.8 4.6 5.2 bottom depth) and decreased in velocity both sho- 30°S 2.1 1.4 1.7 reward and seaward.